Method for improving ground

ABSTRACT

A method for improving ground is capable of improving the strength or quality of an underground consolidated body formed by reducing the ratio of water to a “rich-mixed” solidification material (a cement) (W/C), assuredly carrying the solidification material from a feed source to a jet device, and reducing the amount of solidification material treated as an industrial waste in a construction process. The method for improving ground includes a step of drilling a drilling hole in the ground to be improved, a step of moving (pulling up) a jet device in a vertical direction by rotating the same while the jet device is inserted into the drilling hole and a fluid for cutting the ground (a stable liquid or a partition forming material) is injected from the jet device, and a step of injecting a solidification material from the jet device.

TECHNICAL FIELD

The present invention relates to a ground improvement technology thatforms an underground consolidated body by cutting (in-situ) soil in theground to be improved and mixing water and a solidification materialsuch as cement and agitating a mixture thereof.

BACKGROUND

A technology for forming an underground consolidated body of acylindrical shape by drilling a drilling hole in a ground to beimproved, moving (pulling up or pushing down) a jet device in a verticaldirection by rotating the same while the jet device is inserted into thedrilling hole and a high-pressure fluid such as water is injected in anoutward radial direction from the jet device to cut an in-situ soil, andby mixing the cut soil and a solidification material such as a cementand agitating a mixture thereof by injecting or delivering thesolidification material to the soil has widely been known (e.g. PatentDocument 1).

In order to improve the strength (quality) of an undergroundconsolidated body formed, it is preferable that the ratio of water to asolidification material (a cement) to be fed (W/C) be low, or thesolidification material be so called “rich-mixed.”

However, a lower W/C might lead to more viscosity of a mixture of waterand a cement, thereby blocking a carrying passage from a cement feedsource to a jet device. Thus, it is difficult to carry a solidificationmaterial to the jet device.

In addition, all of a solidification material injected from a jet deviceis not solidified underground and large amounts of the solidificationmaterial are discharged above the ground as a slurry. In fact, such asolidification material must be treated as an industrial waste. Also, ifa solidification material is “rich-mixed” with a low W/C, large amountsof the solidification material will be treated as an industrial waste,resulting in an increase in construction costs accordingly.

From the above described reasons, use of a “lean-mixed” solidificationmaterial with a W/C of 100% or more has been essential in a prior art.

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: JP-A-7-331652

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

The present invention was created in view of the above situation, andhas an object to provide a a method for improving ground being capablefor improving the strength or quality of an underground consolidatedbody formed by reducing the ratio of water to a “rich-mixed”solidification material (a cement) (W/C), assuredly carrying thesolidification material from a feed source to a jet device, and reducingthe amount of the solidification material treated as an industrialwaste.

Means for Solving the Problem

A method for improving ground of the present invention comprises: a stepof drilling a drilling hole (H) in a ground to be improved (G); a stepof moving (pulling up) a jet device (1) in a vertical direction byrotating the same while the jet device (1) is inserted into the drillinghole(H) and a fluid for cutting the ground (G) (a stable liquid or apartition forming material) is injected from the jet device (1); and astep of injecting a solidification material from the jet device (1),wherein said step of moving (pulling up) the jet device (1) in avertical direction by rotating the same while the fluid (the stableliquid or the partition forming material) for cutting the ground (G) isinjected from the jet device (1) comprises: a step of cutting the ground(G) by injecting the partition forming material; and a step of injectinga solidification material (C) while the ground (G) is cut by injectingthe stable liquid after injecting the partition forming material.

The method for improving ground of the present invention preferablycomprises: a step of collecting a mixture of a stable liquid dischargedabove the ground and a cut soil (S: slurry) by a slurry collectingstructure (2); and a step of carrying the slurry (S) collected by theslurry collecting structure (2) to a slurry treating structure (4) andadding an enzyme (E: a cellulose decomposition enzyme such as“cellulase”) from an enzyme feed source (5).

In addition, the method for improving ground of the present inventioncan be applied to purify contaminated water, which comprises: a step ofdrilling a drilling hole (H) in a ground to be improved (G); and a stepof moving (pulling up) a jet device (1) in a vertical direction byrotating or pivoting the same while the jet device (1) is inserted intothe drilling hole (H) and a fluid (a stable liquid or a partitionforming material) for cutting the ground (G) is injected from the jetdevice (1); the fluid is injected injects zeolite from the jet device(1) in said step of moving the jet device (1) in a vertical direction.

Effect of the Invention

The method for improving ground of the present invention comprising theabove steps can improve the strength(quality)of an undergroundconsolidated body formed from a rich-mixed solidification material whoseratio of water to a cement (W/C) ranges from 26% to 40%, compared to thestrength of an underground consolidated body formed with a conventionallean-mixed solidification material.

Herein, a solidification material (a rich-mixed solidification materialwhose W/C ranges from 26% to 40%) contains a high fluidity, and anincrease in the viscosity of even a rich-mixed solidification materialis reduced. Thus, the method for improving ground of the presentinvention can carry a rich-mixed solidification material by means of apump for carrying a lean-mixed solidification material used in a priorart.

According to the present invention, if a partition forming material isinjected prior to a step of cutting soil with a stable liquid, aseparation layer (L_(D)) composed of the partition forming material isformed between a layer (L_(W)) of a mixture of the stable liquid and acut soil and a layer (L_(C)) of a rich-mixed solidification material.

By using the separation layer (L_(D): the layer composed of thepartition forming material), the rich-mixed solidification materialinjected underground can reduce contact with the mixture of the stableliquid and the cut soil.

Therefore, only the mixture of the stable liquid and the cut soil isdischarged above the ground as a slurry (S), and the rich-mixedsolidification material is scarcely discharged above the ground.Specifically, the layer of the partition forming material (L_(D): theseparation layer) can reduce discharge of the solidification materialinjected underground above the ground.

Since discharge of the solidification material above the ground as aslurry (S) is reduced, the method for improving ground of the presentinvention can reduce the amount of a solidification material dischargedabove the ground as a slurry (S) in comparison with a prior art, therebysaving construction costs accordingly.

The method for improving ground of the present invention can collect amixture of a stable liquid and a cut soil (S: slurry)ejected above theground by including a step of collecting the slurry (S) discharged abovethe ground by a slurry collecting structure (2).Therefore, it ispossible to prevent the slurry (S) from dispersing around a constructionsite and working conditions from deteriorating.

In addition, by including a step of carrying the slurry (S) collected bythe slurry collecting structure (2) to a slurry treating structure (4)and adding an enzyme (E: a cellulose decomposition enzyme such as“cellulase”) from an enzyme feed source (5), the slurry (S) as a mixedsolution of the stable liquid and the cut soil will turn into a mixedsolution of only water and soil after guar gum (a natural water-solublepolymer material) in the stable liquid is degraded by the cellulosedecomposition enzyme (E). Herein, since the method for improving groundof the present invention is not required to treat a slurry as anindustrial waste, if it is a mixed solution of only water and soil, itis not necessary to transport by land the slurry to a treating facilityaccordingly, as opposed to a prior art.

In a step of moving (pulling up) a jet device (1) in a verticaldirection by rotating or pivoting the same while a fluid for cutting theground (G) (a stable liquid or a partition forming material) is injectedfrom the jet device (1) according to the present invention, zeolite isinjected from the jet device (1) to form a zeolite layer (L_(Z): azeolite bottom slab) underground.

When said zeolite bottom slab (L_(Z)) is placed underground at anoutflow (leakage) passage or a diffusion passage of a ground water(W_(G)) contaminated with a radioactive material in an adjacent facilitysuch as a reactor building (21),the ground water (W_(G)) contaminatedwith the radioactive material that flows out or diffuses undergroundfrom the reactor building (21) or others comes into said zeolite bottomslab (L_(z)) in the process of underground outflow or diffusion andpasses (or transmits) said zeolite bottom slab (L_(z)).

In the process of the ground water (W_(G)) to pass (transmit) thezeolite bottom slab (L_(z)), most cesium mainly contained in theradioactive material is adsorbed by zeolite to be removed from theground water. Consequently, the concentration of the radioactivematerial in the ground water that passes (transmits) said zeolite bottomslab (L_(z)) is significantly reduced to a “standard value” or less.Specifically, the method for improving ground of the present inventionalso serves as a method for purifying ground water contaminated with aradioactive material.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view showing an embodiment of the presentinvention;

FIG. 2 is a process drawing showing a first step for implementing anembodiment;

FIG. 3 is a process drawing showing a step following a step shown inFIG. 2;

FIG. 4 is a cross sectional view of a jet device taken from line A-A ofFIG. 3;

FIG. 5 is a process drawing showing a step following a step shown inFIG. 3;

FIG. 6 is process drawing showing a step following a step shown in FIG.5;

FIG. 7 is a flow chart showing the procedures shown in FIGS. 2 to 6;

FIG. 8 is a view showing the problem to be solved by the anotherembodiment of the present invention;

FIG. 9 is a schematic view showing another embodiment of the presentinvention; and

FIG. 10 is a process drawing showing a step of another embodiment of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described with referenceto the drawings.

First, an apparatus required for implementing an embodiment for themethod for improving ground will be described with reference to FIG. 1.

In FIG. 1, the ground to which the method for improving ground of thepresent invention is applied is denoted by a symbol G. A rod-shaped jetdevice 1 is inserted into a drilling hole H drilled in a ground G.

Herein, a installing mechanism 6 shown by dotted line in FIG. 1 is anapparatus for inserting (installing) the jet device 1 into the drillinghole H.

The jet device 1 is a double-pipe structure (FIG. 4, not shown in FIG. 1in detail). In FIG. 4, an inner space of an inner pipe 15 provides aflow passage for feeding a rich-mixed solidification material. Anannular space between the inner pipe 15 and an outer pipe 16 provides aflow passage for feeding as table liquid or a partition formingmaterial.

In FIG. 1, a lower end portion of the jet device 1 is provided with adischarge port 11 (a jetting port) of a solidification material. Aportion which is vertically higher than the lower end portion of the jetdevice 1 is provided with a plurality of jetting ports 12such as nozzles(2 jetting ports in FIG. 1).

On a horizontal cross section of the jet device 1, a plurality ofjetting ports 12 (2 jetting ports in FIG. 1) are disposed so as to besymmetrical with respect to the central axis in a vertical direction(not shown). A plurality of jetting ports 12 are provided to inject thestable liquid or the partition forming material.

The stable liquid and the partition forming material are notsimultaneously injected from a plurality of the jetting ports 12.Asshown in FIGS. 5 and 6 and later descriptions, the partition formingmaterial is injected from the jetting ports 12 prior to a step ofcutting soil by injecting the stable liquid from a plurality of saidjetting ports 12.

As shown in FIG. 1, a separation layer L_(D) composed of a mixture ofthe partition forming material and a cut soil is formed between a layerL_(W) of a mixture of the stable liquid and the cut soil and a layerL_(C) of a (rich-mixed) solidification material.

In FIG. 1, the separation layer L_(D) composed of the partition formingmaterial is formed after a step of forming a separation layer L_(D) byinjecting the partition forming material, and soil is cut by injecting ajet flow J of the stable liquid from the jetting ports 12.Herein, thesolidification material is delivered (injected) from the discharge port11 at a lower end of the jet device 1 to form the layer L_(C) of thesolidification material.

In an embodiment shown in drawings, a solution containing 5% by weightof a viscosity improver such as guar gum of a natural water-solublepolymer material is injected from the jet device 1 and a plurality ofthe jetting ports 12 as the stable liquid to drill soil.

In an embodiment shown in drawings, the partition forming material is asolution containing 5% by weight of a viscosity improver such as guargum of a natural water-soluble polymer material and 5% by weight ofsodium silicate (water glass).The partition forming material is theninjected in the soil and mixed with field soil to provide a separationlayer L_(D).

The solidification material is a mixture of water and a rich-mixedcement in an embodiment shown in drawings, such as a mixture whose W/Cranges from 26% to 40%. The theoretical value of W/C is determined at26% and a lower limit. On the other hand, inventors of the presentinvention experimentally failed to obtain a desired strength (quality)on an underground consolidated body when W/C was over 40%.

In an embodiment shown in drawings, a high plasticizer is added to thesolidification material (W/C ranges from 26% to 40%). Addition of a highplasticizer can reduce an increase in the viscosity of a rich-mixedsolidification material whose W/C ranges from 26% to 40%, and it ispossible to carry the rich-mixed solidification material (W/C rangesfrom 26% to 40%) by using a conventional pump for carrying a lean-mixedsolidification material.

In an embodiment shown in drawings, 3 to 7% by weight of polycarboxylicacid-based compound (e.g. Product from TAKEMOTO OIL&FAT Co., Ltd.“Chu-po-ru” series) is added to a cement as a high fluidity. Inventorsof the present invention experimentally added 5% by weight of apolycarboxylic acid-based compound to a cement, and found that it ispreferable in carrying a solidification material of an undergroundconsolidated body.

Inventors of the present invention experimentally found that a mixtureobtained by mixing 100 parts by weight of a cement, 25parts by weight ofwater and 5 parts by weight of a polycarboxylic acid-based compound andagitating a mixture thereof can be carried by using a conventional pumpfor carrying a lean-mixed solidification material (W/C is 100% or more).

In FIG. 1, the jet device 1 is connected to a partition forming materialfeed source 7 via an introduction portion 14 and a feed line 17, andconnected to a stable liquid feed source 8 via the introduction portion14 and a feed line 18. The jet device 1 is connected to a solidificationmaterial feed source 9 via the introduction portion 13 and a feed line19.

A change-over valve 10 is placed on feed lines 17, 18 and 19. Byswitching the change-over valve 10, the partition forming material, thestable liquid and the solidification material are each fed to the jetdevice 1 or feeding is quenched.

As shown in FIG. 1, formation of a separation layer L_(D) is completed.Soil is cut by injecting the stable liquid, and the solidificationmaterial is delivered (injected) to form a layer L_(C) of thesolidification material. Thus, in FIG. 1, while the change-over valve 10cuts off feeding of the partition forming material from a partitionforming material feed source 7 to the jet device 1, the change-overvalve 10 is at a switching position for feeding the stable liquid fromthe stable liquid feed source 8 to the jet device 1 and thesolidification material from the solidification material feed source 9to the jet device 1.

In place of the change-over valve 10, the partition forming material,the stable liquid and the solidification material can be controlled infeed/feed-quenching by ON-OFF control of a pump of the partition formingmaterial feed source 7 (not shown), a pump of the stable liquid feedsource 8 (not shown), a pump of the solidification material feed source9 (not shown).

As described above, the jet device is moved (e.g. pulled up) in avertical direction by rotating the same (i.e. rotating a inject nozzlein a injecting direction) while high-pressure water and a solidificationmaterial are injected from the jet device. In this case, a conventionalmethod for improving ground subjects a solidification material toreverse flow above the ground as a slurry of a mixture of water, soiland a solidification material and to discharge above the ground.

On the other hand, in an embodiment shown in FIG. 1, a layer L_(W) of amixture of the stable liquid and the cut soil and a layer L_(C) of arich-mixed solidification material are divided by a layer L_(D) (aseparation layer) of a mixture of the partition forming material and thecut soil. Therefore, the layer L_(D) of the stable liquid for cuttingsoil hardly mixes with the layer L_(C) of the rich-mixed solidificationmaterial via the separation layer L_(D).

As the rich-mixed solidification material is injected and the size ofthe solidification material layer L_(C) in a vertical directionincreases (becomes thick), the layer L_(D) (the separation layer) of thepartition forming material will move upward.

Consequently, the mixture of the stable liquid and the cut soil isdischarged above the ground (as a slurry), and excess of thesolidification material on the solidification material layer L_(C) viathe separation layer L_(D) to be discharged above the ground is reducedor removed.

Specifically, in an embodiment shown in drawings, discharge of the(rich-mixed) solidification material delivered (injected) in the soil bythe layer L_(D) (the separation layer) of the partition forming materialabove the ground is reduced. Thus, in an embodiment shown in drawings,while a slurry discharged (subjected to reverse flow) above the groundcontains the stable liquid and the cut soil, discharge of thesolidification material above the ground as a slurry can be reduced.

Herein, the thickness of the layer L_(D) (the separation layer) of thepartition forming material is equal to a distance L in a verticaldirection between the discharge port 11 of the solidification material(the discharge port at a lower end portion of the jet device 1) and thejetting ports 12 for ejecting the stable liquid or the partition formingmaterial (a plurality of jetting ports provided upward from thedischarge port 11).

The vertical distance L between said discharge port 11 and the jettingports 12 is defined as a thickness (the size in a vertical direction)required for dividing the layer L_(W) of the mixture of the stableliquid and the cut soil and the layer L_(C) of the rich-mixedsolidification material by the separation layer L_(D) composed of thepartition forming material and preventing the rich-mixed solidificationmaterial from mixing with the mixture of the stable liquid and the cutsoil.

In an embodiment shown in drawings, the thickness L (the distance in avertical direction) is determined at 1 m.

A surface portion of the drilling hole H is provided with a slurrycollecting structure 2.

In FIG. 1, a slurry is ejected above the ground via a sectional annularspace between an inner wall surface of the drilling hole H and the jetdevice 1.

In FIG. 1, the slurry collecting structure 2 collects slurry dischargedabove the ground. Thus, dispersion of the slurry around a constructionsite and deterioration of working conditions can be prevented.

A known technology may be applied as for the slurry collecting structure2.

Slurry collected in the slurry collecting structure 2 is fed to theslurry treating structure 4 via a slurry carrying line 3. An enzyme (acellulose decomposition enzyme such as “cellulase”) is added from anenzyme feed source 5 to the slurry fed to the slurry treating structure4.

Herein, since a prior art shows that a slurry discharged above theground contains a solidification material, the slurry must be treated asan industrial waste. Nevertheless, as described above with reference toFIG. 1, the slurry fed to the slurry treating structure 4 is a mixedsolution of the stable liquid and the cut soil to prevent thesolidification material from being contained. Therefore, in FIG. 1, whena cellulose decomposition enzyme is added to the slurry fed to a slurrytreating structure 4, guar gum (a natural water-soluble polymermaterial) in the stable liquid is degraded by the cellulosedecomposition enzyme and the slurry will turn into a mixed solution ofwater and soil. This type of solution does not correspond to anindustrial waste, and it is thus not necessary to transport the mixedsolution to an treating facility as an industrial waste.

Subsequently, with reference to FIGS. 2 to 7, operational processes ofthe above-mentioned method for improving ground will be described.

FIG. 2 shows that a drilling hole H is drilled in a ground G to beimproved. A jet device 1 is inserted into the drilling hole H.

In FIG. 2, an internal diameter D_(H) of the drilling hole H is largerthan an external diameter of the jet device 1 to be inserted. Herein,when soil of the ground G is cut with a stable liquid, a slurry isdischarged (subjected to reverse flow) above the ground via a sectionalannular space between an inner wall surface of the drilling hole H andan outer peripheral surface of the jet device 1. The internal diameterD_(H) of the drilling hole H is determined at a value so that the slurryis smoothly discharged above the ground.

The depth of the drilling hole H (L_(H)) is determined according to thedepth of the soil to be improved.

In FIG. 3 showing a step following a step shown in FIG. 2, a rod-shapedjet device 1 is inserted into a drilling hole H. When the jet device 1is inserted into the drilling hole H, a known installing mechanism 6 isemployed.

FIG. 4 is a cross sectional view showing jetting ports 12 of the jetdevice 1 taken from line A-A of FIG. 3. FIG. 4 shows only the jet device1, not a sectional view of the drilling hole H. As shown in FIG. 4, thejet device 1 is a double-pipe structure composed of an inner pipe 15 andan outer pipe 16. A solidification material flows inside the inner pipe15, and a stable liquid or a partition forming material flows via aspace between the inner pipe 15 and the outer pipe 16.

In fact, the stable liquid or the partition forming material is notsimultaneously injected. Either of them is injected according to acorresponding step. An introduction portion 14 of the stable liquid orthe partition forming material is connected to a plurality of jettingports 12 via an annular space (FIG. 4) between the inner pipe 15 and theouter pipe 16 of the jet device 1 and a pipe (not shown).

FIG. 3 shows that the jet device 1 is inserted into the drilling hole H,and none of the solidification material, the stable liquid or thepartition forming material are injected or delivered in the soil.

Upon injecting of the stable liquid or the partition forming material,in order to pull upwardly the jet device 1 by rotating the same on acentral axis in a longitudinal direction, structures (a rotatingstructure and a lifting structure, not-shown in drawings) are providedin the installing mechanism 6.

In FIG. 3, a slurry collecting structure 2 provided at a surface portionof the drilling hole H is connected to an annular space between an innerwall surface of the drilling hole H and an outer peripheral surface ofthe jet device 1 to collect a slurry ejected above the ground. Theslurry collecting structure 2 is operated by a drive mechanism (notshown).

FIG. 5 is a process drawing showing a step following a step shown inFIG. 3 and shows that a partition forming material is injected to cut aground G. In FIGS. 5 and 6, a installing mechanism 6 is not shown.

In FIG. 5, the partition forming material is introduced at anintroduction portion 14 to the jet device 1 from a partition formingmaterial feed source 7 via a change-over valve 10 and a feed line 17.Thepartition forming material is injected underground from a plurality ofjetting ports 12 in an outward radial direction as a jet flow J via anannular space (FIG. 4) between an inner pipe 15 and an outer pipe 16.

Thereafter, the jet device 1 injects the jet flow J of the partitionforming material to cut the ground G, and moves (pulls up)in a verticaldirection by rotating the same. Consequently, a layer L_(D) (aseparation layer) of a mixture of the partition forming material and acut soil is formed. As described with reference to FIG. 1, prior to astep of cutting the soil by injecting the stable liquid, the partitionforming material is injected to form a separation layer L_(D) composedof the partition forming material so as not to mix but separate an layerL_(W) of a mixture of the stable liquid and the cut soil and a layerL_(C) of a solidification material.

As shown in FIG. 5, in a step of cutting a ground G by injecting thepartition forming material, a change-over valve 10 is opened only in afeed line 17 from a partition forming material feed source 7 to the jetdevice 1 and closed in feed lines 18 and 19 from a stable liquid feedsource 8 and a solidification material feed source 9 to the jet device1.Thus, only the partition forming material is fed to the jet device 1,and the stable liquid and the solidification material are not fed to thejet device 1.

Herein, in a step of cutting the ground G by injecting the partitionforming material, a slurry as a mixture of the partition formingmaterial and a cut soil is generated and subjected to reverse flow abovethe ground. Slurry subjected to reverse flow above the ground iscollected by the slurry collecting structure 2.

If the jet device 1 is pulled up until the thickness of the layer L_(D)(the separation layer)of the partition forming material comes to aspecific size L (the thickness required for dividing the layer L_(W) ofa mixture of the stable liquid and the cut soil and a rich-mixed layerL_(C) of the solidification material and reducing mixture with a mixtureof the stable liquid and the cut soil by the rich-mixed solidificationmaterial: 1 m in an embodiment shown in drawings), a step shown in FIG.5 will be completed and a step shown in FIG. 6 will be started.

In a step shown in FIG. 6, the solidification material is injected whilethe ground G is cut by injecting the stable liquid. In a step shown inFIG. 6, while the change-over valve 10 cuts off a feed line 17 from thepartition forming material feed source 7 to the jet device 1, it opens afeed line 18 from the stable liquid feed source 8 to the jet device 1and a feed line 19 from a solidification material feed source 9 to thejet device 1.

Accordingly, the stable liquid fed via the change-over valve 10 in thefeed line 18 from the stable liquid feed source 8 is injected in anoutward radial direction in underground from a plurality of jettingports 12 via an annular space (FIG. 4) between an inner pipe 15 and anouter pipe 16 from an upper introduction portion 14 of the jet device 1.The solidification material is introduced into the jet device 1 from ansolidification material introduction portion 13 upward from the jetdevice 1 via a feed line 19 and the change-over valve 10 from thesolidification material feed source 9, and delivered underground from adischarge port 11 via an internal space of the inner pipe 15 (FIG. 4).

The stable liquid is injected from the jet device 1 as a jet flow J tocut a ground G. The jet device 1 is pulled up in an upward verticaldirection by rotating the same.

Meanwhile, the solidification material is delivered (injected) from thedischarge port 11 provided at a lower end of the jet device 1.Thereafter, an in-situ soil and the solidification material are mixed toform an underground consolidated body.

The stable liquid is injected underground from the jet device 1 to cutand agitate the ground G, and the jet device 1 is pulled up in avertical direction by rotating the same on an axis of the jet device 1to form the layer L_(W) of a mixture of the stable liquid and the cutsoil. Then, the solidification material is delivered (injected)underground from the jet device 1 to form the layer L_(C) of thesolidification material (an underground consolidated body).

As described above, since the separation layer L_(D) composed of thepartition forming material is placed between the layer L_(W) of amixture of the stable liquid and the cut soil and the layer L_(C) of thesolidification material, mixture of the layer L_(W) of a mixture of thestable liquid and the cut soil and the layer L_(C) of the solidificationmaterial are not mixed.

As the solidification material is continuously delivered (injected) fromthe jet device 1 and the size of the layer L_(C) of the solidificationmaterial in a vertical direction increases (becomes thick), the layer ofthe partition forming material (the separation layer L_(D)) will moveupward.

Thus, a slurry (a mixture of the stable liquid and the cut soil) isdischarged above the ground only from an upper region of the separationlayer L_(D) composed of the partition forming material, or the layerL_(W) of a mixture of the stable liquid and the cut soil. A rich-mixedsolidification material in the layer L_(C) of the solidificationmaterial is scarcely discharged above the ground.

Since the solidification material is not discharged above the ground ina step shown in FIG. 6, a slurry collected by a slurry collectingstructure 2 is enzyme-degraded by the slurry treating structure 4, andit will turn into a mixture of soil and water. Accordingly, the troubleof treating the same by using a dedicated treating facility can be savedas an industrial waste.

The step shown in FIG. 6 is continued until the layer L_(C) of thesolidification material (the underground consolidated body) comes abovethe ground and a size of an underground consolidated body in a verticaldirection reaches a predetermined value.

FIG. 7 is a flow chart showing steps shown in FIGS. 2 to 6.

With reference to the flow chart in FIG. 7 in particular and FIGS. 2 to6, construction procedures of the embodiment shown in drawings will bedescribed.

In FIG. 7, in step S1, a change-over valve 10 is switched to open only afeed line 17 from a partition forming material feed source 7 to the jetdevice 1, and a feed line 18 from a stable liquid feed source 8 and afeed line 19 from a solidification material feed source 9 are closed tofeed a partition forming material to the jet device 1.Then, while apartition forming material is injected underground from jetting ports12, the jet device 1 is pulled up in a vertical direction by rotatingthe same, thereby forming a separation layer L_(D) composed of thepartition forming material. Thereafter, the process proceeds to step S2.

In step S2, whether the thickness of the separation layer L_(D) composedof the partition forming material reaches a required thickness (a sizein a vertical direction L: predetermined size) or not is determined. Inother words, in step S2, whether the amount of pulling up the jet device1 is a predetermined size L or more or not is determined.

If the amount of pulling up the jet device 1 (the thickness of theseparation layer L_(D)) is less than the thickness L required for theseparation layer L_(D) (step S2 is determined “NO”), the process willreturn to step S1 to continue a step of injecting the partition formingmaterial and cutting the ground G to form the separation layer L_(D).

On the other hand, the amount of pulling up the jet device 1 (thethickness of the separation layer L_(D)) is the thickness L required forthe separation layer L_(D) or more (step S2 is determined “YES”), theprocess will proceed to step S3.

In step S3, the change-over valve 10 is switched to close a feed line 17from a partition forming material feed source 7 to the jet device 1 andto open a feed line 18 from a stable liquid feed source 8 to the jetdevice 1 and a feed line 19 from a solidification material feed source 9to the jet device 1. Accordingly, injecting of the partition formingmaterial is quenched, and the stable liquid is injected in a horizontaldirection to deliver a solidification material.

Thereafter, the jet device 1 is pulled up in a vertical direction byrotating the same while the stable liquid is injected to cut the groundG. At the same time, the solidification material is delivered (injected)from a discharge port 11 provided at a lower end of the jet device 1,and it is mixed with a cut in-situ soil to form an undergroundconsolidated body.

A slurry (a mixed fluid of the stable liquid and the cut soil) generatedin step S3 is collected above the ground by using a collecting structure2, carried to a slurry treating structure 4 by using a slurry carryingline 3, and an enzyme is added from an enzyme feed source 5 in theslurry treating structure 4 to provide a mixed solution only composed ofwater and soil. Therefore, it is not necessary to transport the same toa treating facility as an industrial waste.

Then, the process will proceed to step S4.

In step S4, whether a layer L_(C) of the solidification material reachesabove the ground so that the size of an underground consolidated body ina vertical direction is a desired size to complete the formation of anunderground consolidated body or not is determined.

If the layer L_(C) of the solidification material (the undergroundconsolidated body) does not reach a desired thickness and the formationof the underground consolidated body is not completed (step S4 isdetermined “NO”), the process will return to step S3 to continue a stepof delivering (injecting) the solidification material while the stableliquid is injected to cut the ground G.

If the layer L_(C) of the solidification material reaches a desired sizein a vertical direction and the formation of the undergroundconsolidated body is completed (step S4 is determined “YES”), theprocess will proceed to step S5.

In step S5, a change-over valve 10 is switched to close a feed line 18from a stable liquid feed source 8 to the jet device 1 and a feed line19 from a solidification material feed source 9 to the jet device 1 toquench the feeding of a stable liquid and a solidification material tothe jet device 1.

In addition, an operation for rotating the jet device 1 and an operationfor pulling up the same above the ground at a predetermined speed arequenched.

Since a passage from the partition forming material feed source 7 to thejet device 1 is closed instep S3, the partition forming material is notfed by the jet device 1 even in step S5.

Thereafter, operations of a slurry collecting structure 2, a slurrycarrying line 3 and a slurry treating structure 4 are quenched, and theprocess will proceed to step S5 to complete the operations.

According to the embodiment shown in drawings, use of a rich-mixedsolidification material (C) whose ratio of water to a cement (W/C)ranges from 26% to 40% can improve the strength (quality) of anunderground consolidated body formed, compared to a solidificationmaterial of a conventional lean-mixed solidification material (W/C is100% or more).

Herein, since a solidification material (C: a rich-mixed solidificationmaterial whose W/C ranges from 26% to 40%) contains a high fluidity, anincrease in the viscosity of the solidification material (C) is reduced,and it can be carried by using a conventional solidification materialcarrying pump (a pump for carrying a lean-mixed solidification materialin a prior art).

In the embodiment shown in drawings, a step S1 for injecting thepartition forming material to form a separation layer L_(D) composed ofthe partition forming material is implemented prior to step S3 forcutting soil with a stable liquid, a layer L_(W) of a mixture of thestable liquid and the cut soil and a rich-mixed layer L_(C) of thesolidification material are divided by a separation layer L_(D).Accordingly, contact of a rich-mixed solidification material with amixed fluid of the stable liquid and the cut soil (a mixed liquidcomprising a layer L_(W)) is reduced, and only a mixed fluid of thestable liquid and the cut soil (a mixed liquid composed of a layerL_(W)) is discharged above the ground as a slurry. Therefore, since therich-mixed solidification material is scarcely discharged above theground, consumption of the solidification material can be reducedcompared to a conventional level.

Furthermore, in the embodiment shown in drawings, since a mixture of thestable liquid and the cut soil discharged above the ground is collectedby a slurry collecting structure 2, no contamination around aconstruction site from a slurry ejected above the ground is found.

The slurry collected by the slurry collecting structure 2 (a mixture ofthe stable liquid and the cut soil) is carried to a slurry treatingstructure 4 to add a cellulose decomposition enzyme from an enzyme feedsource 5, thereby turning the slurry into a mixed solution of only waterand soil as non-industrial waste. Thus, it is not necessary to transportthe same to a treating facility, which can save costs for treating aslurry.

Herein, diffusion of ground water contaminated with a radioactivematerial (e.g. around a reactor building) has recently become a problemin society. Another embodiment as opposed to the ones described in FIGS.1 to 7 is capable of solving the problem.

Herein, with reference to FIG. 8, the above described problem (diffusionof ground water contaminated with a radioactive material) will bedescribed.

In FIG. 8, in cases where a ground water WG1 contaminated with aradioactive material from a reactor building 21 (including a storagefacility for a radioactive material and groundwater: the same as above)flows out (leaks) in the ground G, a continuous wall 22 (e.g. a frozensoil wall) is formed so as to surround the reactor building 21.Specifically, the flow of the ground water WG1 containing a radioactivematerial subjected to outflow and diffusion underground from the reactorbuilding 21 is cut off by using the continuous wall 22. Accordingly,outflow and diffusion of the ground water WG1 contaminated to theoutside thereof through the frozen soil wall 22 is prevented.

A symbol 23 in FIG. 8 represents a device for forming a frozen soilwall.

However, use of only the continuous wall 22 fails to prevent diffusionof the contaminated ground water WG2 subjected to outflow(leakage)underground in a direction just below the reactor building 21from the same.

As obviously shown in FIG. 8, this is because that the flow of thecontaminated groundwater WG22 running underground more deeply than thecontinuous wall 22 cannot be prevented.

An embodiment for solving the problem will be described with referenceto FIGS. 9 and 10.

As shown in FIG. 9, according to the construction method of anembodiment shown in FIGS. 1 to 7, a layer of zeolite (L_(z): a zeolitebottom slab) extending in a horizontal direction is formed in the groundG and below the reactor building 21.

The thickness B of the zeolite bottom slab L_(z), while the ground waterWG2 contaminated with the radioactive material passes (transmits) thezeolite bottom slab L_(z), is determined at a value so that cesiumcontained in the groundwater WG2 can sufficiently be adsorbed by zeoliteof the zeolite bottom slab L. The thickness depends on the degree ofcontamination and several working conditions.

In addition, the range of the zeolite bottom slab L_(z) in a horizontaldirection is determined so that passages for outflow and diffusion ofthe groundwater WG2 contaminated with the radioactive material subjectedto outflow (leakage) from the from reactor building 21 can assuredlypass the zeolite bottom slab L_(z).

When the zeolite bottom slab L_(z) shown in FIG. 9 is formed, the groundwater WG2 subjected to outflow (leakage) and diffusion underground in adirection just beneath the reactor building 21 from the same passes thezeolite bottom slab L_(z) to adsorb and remove cesium. This is becausezeolite has a chemical property of adsorbing cesium as a main componentof the radioactive material. Herein, since cesium is a major componentof the radioactive material, and if cesium can be removed, theradioactive material concentration in the ground water WG2 is reduced toa safety value (or a standard value or less).

The ground water WG1 running upward from the zeolite bottom slab L_(z)is cut off by a continuous wall 22, resulting in no diffusion.

In order to prevent diffusion of the contaminated ground water WG2, thecontinuous wall 22 and the zeolite bottom slab L_(z) are connected toeach other.

According to similar procedures of embodiments shown in FIGS. 1 to 7,FIG. 10 shows formation of the zeolite bottom slab L_(z) extending in ahorizontal direction.

As shown in FIG. 10, a step of drilling a drilling hole H in the groundG and a step of moving (pulling up) a jet device 1 in a verticaldirection by rotating the same while a fluid (a partition formingmaterial) for cutting the ground G is injected from the jet device 1 arethe same as those shown in FIGS. 1 to 7.

The jet device 1 injects a jet flow J of the partition forming materialto cut the ground G, and pulled up in an upward vertical direction byrotating the same. Like in the embodiments in FIGS. 1 to 7, a layerL_(D) (a separation layer) of a mixture of the partition formingmaterial and a cut soil is formed.

In a step shown in FIG. 10, zeolite is delivered underground from adischarge port 11 provided at a lower end of the jet device 1, in placeof a solidification material according to embodiments shown in FIGS. 1to 7.

Since the separation layer L_(D) is placed in this process, the zeolitedelivered does not mix with a stable liquid injected from dischargeports 12 and a cut soil by a jet flow of a stable liquid to form azeolite bottom slab L_(z) extending in a horizontal direction.

In other words, by pulling up the jet device 1 in a vertical directionby rotating the same on an axis thereof while the stable liquid isinjected underground from the jet device 1 to cut and agitate the groundG, like in the embodiments shown in FIGS. 1 to 7, a layer L_(W) of amixture of the stable liquid and the cut soil and the layer L_(D) (theseparation layer) of a mixture of the partition forming material and thecut soil are formed. Thereafter, by delivering (injecting) zeoliteunderground from the jet device 1, a layer L_(z) of zeolite (a zeolitebottom slab) is formed.

Since the separation layer L_(D) composed of the partition formingmaterial is placed between the layer L_(W) of a mixture of the stableliquid and the cut soil and the layer Lz of the zeolite (the zeolitebottom slab), mixture of the stable liquid of and the cut soil in thelayer L_(W) with the layer L_(z) of zeolite (the zeolite bottom slab) isreduced, thereby maintaining a separate situation.

A step shown in FIG. 10 is continued until the layer L_(z) of zeolite(the zeolite bottom slab) has a predetermined depth at a predeterminedposition (depth) in a vertical direction underground.

A cross sectional shape of the layer L_(z) of zeolite (the zeolitebottom slab) (i.e. the range of the zeolite bottom slab L_(z) in ahorizontal direction) is circular like in the embodiments shown in FIGS.1 to 7. However, the shape of the zeolite bottom slab L_(z) can benon-circular (e.g. a semicircle or a sector) in case contaminated wateris diffused.

It must be stated that the present invention is not restricted by thedescription of the embodiments shown in drawings. The embodiments shownin drawings are merely examples so that any embodiments composed ofsubstantially the same technical concept as disclosed in the claims ofthe present invention and expressing a similar effect are included inthe technical scope of the present invention.

EXPLANATION OF LETTERS OR NUMERALS

-   1 . . . Jet device-   2 . . . Slurry collecting structure-   3 . . . Slurry carrying line-   4 . . . Slurry treating structure-   5 . . . Enzyme feed source-   6 . . . Installing mechanism-   7 . . . Partition forming material feed source-   8 . . . Stable liquid feed source-   9 . . . Solidification material feed source-   10 . . . Change-over valve-   11 . . . Discharge port-   12 . . . Jetting port-   13 . . . Solidification material introduction portion-   14 . . . Stable liquid introduction portion and partition forming    material introduction portion-   15 . . . Inner pipe (jet device)-   16 . . . Outer pipe (jet device)-   17 . . . Pipe-   G . . . Ground-   H . . . Drilling hole-   L_(X) . . . Layer of solidification material-   L_(D) . . . Layer of partition forming material(separation layer)-   L_(W) . . . Layer of mixture of stable liquid and cut soil-   21 . . . Reactor building-   22 . . . Continuous wall-   WG1, WG2 . . . Contaminated ground water-   L_(z) . . . Layer of zeolite (zeolite bottom slab)

What is claimed is:
 1. A method for improving ground comprising: a stepof drilling a drilling hole in a ground to be improved; a step of movinga jet device in a vertical direction by rotating the same while the jetdevice is inserted into the drilling hole and a fluid for cutting theground is injected from the jet device; and a step of injecting asolidification material from the jet device, wherein said step of movingthe jet device in a vertical direction by rotating the same while thefluid for cutting the ground is injected from the jet device comprises:a step of cutting the ground by injecting the partition formingmaterial; and a step of injecting a solidification material while theground is cut by injecting the stable liquid after injecting thepartition forming material.
 2. The method according to claim 1, whereinthe method for improving ground comprising: a step of collecting amixture of a stable liquid discharged above the ground and a cut soil bya slurry collecting structure; and a step of carrying the slurrycollected by the slurry collecting structure to a slurry treatingstructure and adding a decomposition enzyme from an enzyme feed source.3. A method for improving ground comprising: a step of drilling adrilling hole in a ground to be improved; and a step of moving a jetdevice in a vertical direction by rotating the same while the jet deviceis inserted into the drilling hole and a fluid for cutting the ground isinjected from the jet device, wherein said step of moving the jet devicein a vertical direction while the fluid is injected injects zeolite fromthe jet device.